The present invention relates to a water soluble polyester suitable for use as a wire enamel or other type of protective coating. In recent years EPA and OSHA have become more insistent and stringent in their regulations concerning solvents and chemicals relative to their photochemical reactivity, toxicity and related health hazards. This has acted as an impetus toward the development of newer polymers that are capable of being solubilized in water that meet these new Federal and State regulations.
Another object is to prepare a non-trimellitic anhydride polyester with improved cut-through and heat shock properties as a wire enamel with a Class F or higher thermal rating.
A preview of prior art in this area is in order to better develop significant differences and features of the present invention over other polymer systems.
To better illustrate significant differences of the present invention over prior art one must consider the type of triol and diol, the critical ratio of these two materials, and the required excess hydroxyl content or the OH/COOH ratio. First of all, the present invention differs from the Laganis Patents U.S. Pat. Nos. 3,974,115 and 4,016,330 on at least five counts. One is that the polyester intermediate of the invention does not contain a tribasic carboxylic acid or more highly functional polycarboxylic aromatic acid to act as a solubilizing site to render it water soluble. Secondly, these polyesters are reacted to a relatively low acid number on the solids of 5-20 vs. an acid number ranging from 50 to 100 on a solids basis for the two cited patents. Thirdly, the range of excess hydroxyl groups is much higher for these new polyesters and ranges from 80 to 200% vs. 20 to 35% for the cited patents. Fourthly, the ratio of diol to triol is critical and no mention is made of this in the cited patents. Fifthly, and lastly, the new wire coating does not employ hydroxymethylated diacetone acrylamide as a crosslinking agent as in the cited patents.
Relative to Meyer-Zalewski patent U.S. Pat. No. 3,342,780, the present invention differs in at least three instances. Firstly, it differs in the OH/COOH ratio wherein the current invention has a minimum ratio starting from 1.8/1 up to a maximum of 3/1 compared to that of the cited patent of 1/1 up to a maximum of 1.6/1. Examples later on will demonstrate that a clear aqueous solution having less than 30% cosolvent cannot be obtained with less than 80% excess OH content. Secondly, there is the critical ratio of diol to triol to achieve water solubility. Thirdly, there cannot be used Tyzor TPT (tetra isopropyl titanate) as it is unstable in water, and there must be used a water soluble titanate such as the triethanol chelate of titanium or the ammonium lactate chelate of titanium to get a suitable wire coating.
There are many differences that distinguish the invention from the Chang patent U.S. Pat. No. 3,959,201, as to the polyester composition and the final blend. In Chang there are only two compositions shown in examples 77 and 102 that use an aromatic dicarboxylic acid, such as isophthalic acid, and none with terephthalic acid. Both of these examples chemically and molar-ratiowise are exactly identical, are linear in nature, and do not have a triol or any other polyhydric alcohol. Also these materials are blended with aminoplasts to cure, whereas the present compositions are not and have a much higher order of thermal stability and usage than that cited in this reference.
In Holzrichter U.S. Pat. No. 3,957,709, great emphasis is placed on the ester intermediate having a hydroxyl functionality of about 3, whereas in the present invention it ranges from 2.0 to 2.2. Further, the present polyesters have a molecular weight range of 800-1300 or 50 to 100% higher than those of Holzrichter and consequently, the polyesters of Holzrichter without a modifying alcohol do need the presence of a cosolvent as their water solubility and dilutibility are limited without it. From a thermal rating and wire properties in general it is absolutely essential to have a triol present. If one calculates the carbon to oxygen ratio (C/O) of THEIC which is 9/6 pr 4.5/3, then it falls outside the scope of this patent on the low end. It may also be noted that the hydantoin glycol, 1,3-hydroxyethyl-5,5 dimethyl hydantoin has a C/O of 9/4 or 6.75/3 and it is at the upper end of Holzrichter's range of about 7/3 which the patent says adversely affects the water solubility of the ester intermediate. This has not been found to be the case with the present polymers. Lastly, and also important, Holzrichter states in claims 1, 6, 7, 8 and 9 the need for an aminoplast and epoxy resin as curatives. Neither is present in the products of the invention as both would be detrimental on long-term thermal aging. The titanate is the only curing agent present in the present aqueous system and in the solvent system there is employed a phenolic and isocyanate intermediate, besides a titanate, as crosslinkers.
Preston U.S. Pat. No. 3,835,121 cites polyesters containing hydantoin radicals and isocyanurate radicals in the polymeric backbone, but no mention is made of the required excess hydroxyl content or its aqueous solubility characteristics in any of its claims. Furthermore, no mention is made of a monohydric alcohol, such as a glycol ether, which is an essential reactant in one alternative in the present invention. The extreme importance of the role that excess hydroxyl content plays in achieving aqueous solubility will be elaborated upon more fully below. Reviewing the six examples of Preston the excess hydroxyl content ranges from a low of approximately 17 to a high of approximately 63%. This is far below the minimum of 80% in the present case where THEIC only is present or where the hydantoin glycol is present alone with a triol other than THEIC. In both instances with a composition of this type a certain amount of cosolvent, namely, in the 10-30% range, is required. With the monohydric alcohol modified composition no cosolvent is necessary. Furthermore, a different titanate is needed, namely, Tyzor TE or other water soluble titanate for the present invention whereas the Preston titanate is not water soluble or stable in the presence of water. In general, the present solvent system is totally different from Preston's, and thus requires significant formulation changes to achieve a desirable and reasonably economical wire enamel system.
The present polyester composition differs from Hosokawa U.S. Pat. No. 4,011,185, in that it contains no aromatic tetracarboxylic acid or anhydride as required in Hosokawa's claims 1, 4 and 10. Furthermore, in the present invention reaction is carried out to an acid number range of 2-20 vs. 70 to 140 and 70 to 100 as cited in claims 14 and 15 of Hosokawa. The needed wire properties would not be obtained at these high acid numbers because of too many oligomers being present at the higher acid values or less reacted polymers. The organic amines used in this patent are not used solely as solubilizing agents, but react with the free carboxyl groups in the polymer to form amides which further distinguishes the present invention from it as applicant employs only tertiary amines as solubilizing agents and as cosolvents since they are amine alcohols. The product of this patent is thus a polyester-amide and not a straight polyester.